update Date fields with user specified time zone instead of host/system/default timezone when it's available - add unit test
refactoring: split converter tests logically instead of testing different converter classes within a same test class - checked test count remains equal to before refactoring
assert that result calendar from DateConverter is set with user specified time zone when available.
Merge pull request #18 from federecio/develop

update Date fields with user specified time zone instead of host/system/default timezone when it's available - add unit test